Unless otherwise indicated herein, the description provided in this section is not itself prior art to the claims is not admitted to be prior art by inclusion in this section.
A typical cellular wireless network includes a number of base stations each radiating to define a respective coverage area in which user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the network may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Further, a cellular wireless network may operate in accordance with a particular air interface protocol or radio access technology, with communications from the base stations to UEs defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) or Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), and Global System for Mobile Communications (GSM), among others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between coverage areas, and other functions related to air interface communication.
In accordance with the air interface protocol, each coverage area may operate on one or more carrier frequencies or “carriers.” Each carrier may be frequency division duplex (FDD), in which the uplink and downlink operate on different respective ranges of frequency (frequency channels), or time division duplex (TDD), in which the uplink and downlink are multiplexed over time on a common range of frequency.
Further, each coverage area may define a number of channels or specific resources for carrying signals and information between the base station and UEs. For instance, on the uplink, certain resources may be reserved to carry access request messages from UEs seeking to gain access to the base station, other resources may be reserved to carry other uplink control signaling such as measurement reports and scheduling requests, and still other resources may be reserved to carry bearer traffic (e.g., application-layer communications) in a manner assigned or scheduled by the base station. And on the downlink, certain resources may be reserved to carry a pilot or reference signal that UEs may detect and measure to evaluate coverage quality, other resources may be reserved to carry scheduling directives, access response messages, and other downlink control signaling, and still other resources may be reserved to carry bearer traffic in a manner assigned or scheduled by the base station.
When a UE is within coverage of a base station, the UE may from time to time transmit to the base station an access request message. The purpose of such an access request message may depend on the air interface protocol and the circumstances. By way of example, a UE may transmit an access request as a request to gain initial access to communication with a base station, such as to transition from an idle state to a connected state for instance or to facilitate handover to the base station. As another example, a UE may transmit an access request as a response to a page message and/or as a request to establish a particular communication connection such as a call or data session. As still another example, a UE may transmit an access request to register or re-register with a base station and/or to provide a location or tracking area update. And as still another example, a UE may transmit an access request to provide the base station with timing advance information or the like, to facilitate positioning or other functions. Once the base station receives a UE's access request, perhaps after further processing by the base station and/or associated infrastructure, the base station may then transmit an access response message to the UE.
By way of example, the access request that a UE transmits to the base station may take the form of a signature or pattern that is randomly selected from a plurality of signatures or patterns. For instance, in an LTE system, 64 signatures, referred to as preambles, are available, and the UE may randomly select one of the preambles to transmit to the base station. Since multiple UEs may be transmitting access requests at the same time, the preamble may serve to differentiate the request transmitted by the UE from other requests originating from different UEs. Once the base station receives the preamble, the base station may transmit an access response message corresponding to the received preamble. Such a response message, for instance, may include an assignment of an initial uplink resource for the UE to use to communicate with the base station. In response to detecting the access response message corresponding to the preamble, the UE may then communicate with the base station on the assigned uplink resource to complete the communication connection.